[mpweiher]

That's exactly my point.

Sure, it is possible to model these things as functions, for example by "passing" the entire world as a "parameter". However, it is an extremely contrived modelling, basically you're hammering the square problem domain into the round function hole with the biggest hammer you can find until it "fits".

It is also possible to model these things as Turing machines, or NAND gates...

[WJW]

The "app-as-function" is not at all contrived though, it has some very concrete applications that make use of the composability advantages that functions have. The [rack-test](https://github.com/rack/rack-test) gem (and similar languages) work exactly like this: they run the "app" part without the "web server" part to enable much easier testing. Rack middlewares similarly treat the enclosed app as just a function taking some specified input and returning some output value.